Heat Insulated Container

ABSTRACT

A heat insulated container, in which the presence of this heat insulation performance can be confirmed from the outward appearance. In a heat insulated container formed by coating a radiation preventing film on at least one surface of an external surface of an internal glass container and an internal surface of an external glass container, disposing the internal container inside the external container with a gap provided therebetween, joining the internal container and the external container, and evacuating the gap to a vacuum and sealing it, an average particle diameter of particles on the surface of the radiation preventing film is made a predetermined value or more. According to the heat insulated container, since the average particle diameter of the particles on the surface of the radiation preventing film is a predetermined value or more, sufficient heat retaining performance can be obtained.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. national phase application under 35 U.S.C. §371 of International Patent Application No. PCT/JP2005/005778, filed Mar. 28, 2005. The International Application was published in Japanese on Oct. 5, 2006 as International Publication No. WO 2006/103739 A1 under PCT Article 21(2), the content of which are incorporated herein in its entirety.

TECHNICAL FIELD

The present invention relates to a heat insulated container, and more specifically, relates to a glass heat insulated container formed by uniting an internal container with an external container and evacuating a gap provided between the internal container and the external container to a vacuum.

BACKGROUND ART

Conventionally, a glass heat insulated container is produced by disposing a glass internal container inside a glass external container with a constant gap provided therebetween, melting the vicinity of the opening area to thereby integrally unite the internal container with the external container, and evacuating the gap to a vacuum to thereby provide a vacuum insulating layer. Moreover an external surface of the internal container is coated with a radiation preventing film such as an ITO film (a substance produced by doping indium (In) oxide with tin (Sn)) so as to decrease movement of heat between the inside and outside of the heat insulated container, and this coating is carried out by means of sputtering, CVD, PVD, and the like (for example, refer to Japanese Unexamined Patent Publication No. 2003-299582).

SUMMARY OF THE INVENTION

However, even when coating of this radiation preventing film is carried out using the same device, the heat retaining performance of the radiation preventing film can vary. For example, when coating of the radiation preventing film is carried out by means of sputtering, even if the other conditions of sputtering are exactly the same, the heat retaining performance of the radiation preventing film can differ before and after replacing targets in some cases.

It is considered that this heat retaining performance is related to the thickness of the radiation preventing film. However, the heat insulated container needs to be cut in order to measure the film thickness and a container that has been cut cannot be used as a product. Therefore, whether or not a heat insulated container has a predetermined heat retaining performance needs to be determined directly, not by measuring the film thickness, but by measuring the temperature of hot water that has been poured into the heat insulated container a few hours prior to measurement, after the heat insulated container has been assembled up to the final process. This examination is time consuming, and results in increased manufacturing cost. Also, even if it is determined that the heat retaining performance of the heat insulated container does not meet a criterion, the radiation preventing film cannot be re-coated on a heat insulated container that has already been completed, and the heat insulated container is discarded. As a result, the overall manufacturing cost increases.

The present invention has been achieved to solve these problems, and it is an object of the present invention to provide a heat insulated container having a constant heat insulation performance, in which the presence of this heat insulation performance can be non-destructively confirmed.

The present inventors earnestly carried out research in order to solve the problems mentioned above and, as a result, have discovered that there is a constant relationship between the average particle diameter of particles of the radiation preventing film surface and its heat retaining performance. Consequently, it has been discovered that a constant performance can be ensured by maintaining this particle diameter at or above a predetermined value, leading to the present invention.

A heat insulated container according to a first aspect of the present invention, is a heat insulated container formed by coating a radiation preventing film on at least one surface of an external surface of an internal glass container and an internal surface of an external glass container, disposing the internal container inside the external container with a gap provided therebetween, joining an opening area of the internal container with an opening area of the external container, and evacuating the gap to a vacuum and sealing it, wherein an average particle diameter of particles on the surface of the radiation preventing film is a predetermined value or more.

A heat insulated container according to a second aspect of the present invention, is a heat insulated container formed by coating a radiation preventing film on at least one surface of an external surface of an internal glass container and an internal surface of an external glass container, disposing the internal container inside the external container with a gap provided therebetween, joining an opening area of the internal container with an opening area of the external container, and evacuating the gap to a vacuum and sealing it, wherein an average particle diameter of particles on the surface of the radiation preventing film on a part present in at least a side portion of the heat insulated container is a predetermined value or more.

A heat insulated container according to a third aspect of the present invention is characterized in that in the foregoing aspects, the predetermined value is 50 nm.

A heat insulated container according to a fourth aspect of the present invention is characterized in that in any one of the foregoing aspects, the film thickness of the radiation preventing film is 150 nm or more.

A heat insulated container according to a fifth aspect of the present invention is characterized in that in any one of the foregoing aspects, the radiation preventing film is an ITO film.

According to the heat insulated container of the present invention, by making the average particle diameter of the particles on the surface of the radiation preventing film to be a predetermined value or more, sufficient heat retaining performance can be obtained. In addition, since the particle diameter can be measured non-destructively by observation from the outside, examination can be made quickly and, in the case where the coating is judged to be insufficient, a film can be formed over the top. Therefore, the examined heat insulated container is not wasted, and the overall manufacturing cost can be reduced as a result.

The portion of the radiation preventing film that greatly influences the heat retaining performance of the heat insulated container is the portion on the side of the heat insulated container. Therefore, as long as the average particle diameter of the surface particles on the portion of the radiation preventing film on at least the side portion of the heat insulating container is a predetermined value or more, sufficient heat retaining performance can be ensured.

Moreover, by making the average particle diameter of the surface particles of the radiation preventing film to be 50 nm or more, a heat insulating container provided with the radiation preventing film, after being filled with 1000 cc of hot water at 95° C. and sealed, and then left in a room of a temperature of 20° C. for six hours, will be able to maintain the temperature of the hot water thereinside at 60° C. or more.

Moreover, by making the thickness of the radiation preventing film to be 150 nm or more, a heat insulating container provided with the radiation preventing film, after being filled with 1000 cc of hot water at 95° C. and sealed, and then left in a room of a temperature of 20° C. for six hours, will be able to maintain the temperature of the hot water thereinside at 60° C. or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a heat insulated container of a preferred embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an ITO particle diameter, heat retaining performance, and the thickness of an ITO film.

FIG. 3 is a graph showing a relationship between an ITO particle diameter, heat retaining performance, and the thickness of an ITO film under conditions different from that of FIG. 2.

FIG. 4 shows enlarged photographs of ITO films of various particle diameters.

DETAILED DESCRIPTION OF THE INVENTION

Hereunder is a description of a preferred embodiment of the present invention, with reference to the accompanying drawings.

FIG. 1 is a sectional view of a heat insulated container 10 in the embodiment of the present invention. As shown in the figure, the heat insulated container 10 of the present embodiment includes a glass internal container 12, and a glass external container 16 arranged outside of the internal container 12 with a gap 14 having a constant width. The external container 16 is formed by joining an upper external container 16 a and a lower external container 16 b with each other, and the internal container 12 and the upper external container 16 a are joined with each other at an opening area 18. The gap 14 between an internal surface of the external container 16 and an external surface of the internal container 12 is maintained in a vacuum state. Furthermore, the external surface of the internal container 12 is coated with an ITO film 20 that serves as a radiation preventing film for reducing heat radiation. This ITO film 20 is coated by means of a sputtering method and the surface thereof, when observed from the outside, has particles having a diameter at or above a predetermined value. The entire surface of the ITO film 20 in the present embodiment has particles of a diameter at or above the predetermined value. However, it is not limited to this, and only the average particle diameter of the surface particles on at least a portion present in a side section 22 of the heat insulated container 10 need to be of a predetermined value or more.

Here, this predetermined diameter refers to the minimum particle diameter at which, even after filling and sealing 1000 cc of hot water at 95° C. inside the heat insulated container provided with the ITO film, the surface of which has particles of a diameter at or above this predetermined value, and then leaving it in a room temperature at 20° C. for six hours, the temperature of the hot water inside the heat insulated container is still maintained at 60° C. or more. In the present specification, the temperature of the hot water after 1000 cc of hot water at approximately 95° C. has been filled in and sealed inside the heat insulated container and the container has been left in a room at 20° C. for six hours, is referred to as the heat retaining performance, and this 60° C. is the minimum temperature that the functionality of a heat insulated container is generally required to achieve.

Therefore, the temperature of the hot water inside the heat insulated container 10 will be measured at 60° C. or more if 1000 cc of the hot water at 95° C. has been filled in and sealed inside the heat insulated container 10 of the present embodiment and the container has been left in a room at 20° C. for six hours.

Thus, the heat insulated container 10 of the present embodiment is a heat insulated container 10 formed by coating the ITO film 20 on the external surface of the glass internal container 12, disposing the internal container 12 inside the external container 16 with the gap 14, joining the internal container 12 and the external container 16, and evacuating the gap 14 to a vacuum and sealing it, wherein the average particle diameter of the particles on the surface of the ITO film 20 is at the predetermined value or more.

According to this heat insulated container 10, by making the average particle diameter of the particles on the surface of the ITO film 20 to be of the predetermined value or more, the heat retaining performance of 60° C. can be obtained. Furthermore, since the particle diameter can be non-destructively examined by external observation, the examination can be carried out quickly. Moreover, even if the coating is determined to be insufficient, a film can be additionally formed on the coated ITO film since it has been non-destructively examined. Therefore, the examined heat insulated container is not wasted, and the overall manufacturing cost can be reduced as a result.

In the present embodiment the ITO film 20 is used as the radiation preventing film. However, the type of the radiant heat preventing film is not limited to this, and it may be a metal oxide (semiconductor) such as ZnO, SiO_(x), SnO₂, or TiO_(x). The average particle diameter of the surface particles of the radiation preventing film in this case is a particle diameter that is at least the minimum particle diameter at which, after filling and sealing 1000 cc of hot water at 95° C. inside a heat insulated container provided with the radiation preventing film, and then leaving it a room at 20° C. for six hours, the temperature of the hot water inside the heat insulated container can be maintained at 60° C. or more. Moreover, in the present embodiment the ITO film 20 is coated on the external surface of the internal container 12. However the surface to be coated is not limited to this, and it may be another surface, for example, the internal surface of the external container 16 or the like.

EXAMPLE 1

An investigation was made into the relationship between: the average particle diameter (ITO particle diameter) of the surface particles of an ITO film; the thickness of the ITO film; and the heat retaining performance of a finished product of a heat insulated container provided with an internal container covered with the ITO film, for the case where the ITO had been sputtered onto the external surface of the internal container in an atmosphere where the weight ratio of argon to oxygen was 76 to 7.

Graph A in FIG. 2 is a graph showing the relationship between heat retaining performance and ITO particle diameter, with the heat retaining performance (° C.) of a heat insulated container on the vertical axis, and the ITO particle diameter (nm) on the horizontal axis. Moreover on the left side of the graph, a heat retaining performance scale is shown. As this graph A shows, in the case of a heat insulated container in which the external surface of the internal container is covered with an ITO film with surface particles of an average particle diameter of 50 nm or more, even after 6 hours, the temperature of the hot water can be maintained at 60° or more. Moreover, even if the particle diameter increases, the temperature retaining performance does not increase proportionately, and above 150 nm the influence of particle diameter on heat retaining performance becomes smaller. In particular, over 200 nm, even if the particle diameter is increased, there is almost no change in the heat retaining performance. Therefore, under the conditions of the present example, the particle diameter is preferably 50 nm or more, and more preferably 60 nm or more. Furthermore, considering sputtering efficiency, the particle diameter is preferably no more than 200 nm, and considering efficiency still further, it is preferably no more than 150 nm.

Furthermore, graph B is a graph showing the relationship between the ITO film thickness and the particle diameter, with the ITO film thickness (nm) shown on the vertical axis, and the diameter of the ITO particles (nm) shown on the horizontal axis as in graph A. The right hand side of the graph shows a scale of the ITO film thickness. This straight line deviates slightly from the actual plot. However, this is because this straight line represents an approximation formula found from the measured values shown in FIG. 3 of an example 2 described below. According to this graph, a particle diameter of 50 nm corresponds to a film thickness of 150 nm, a particle diameter of 60 nm to a film thickness of 200 nm, a particle diameter of 200 nm to a film thickness of 800 nm, and a particle diameter of 150 nm to a film thickness of 600 nm. Therefore, expressing the conditions of the above particle diameters as film thicknesses, the ITO film is preferably 150 nm or more, and more preferably 200 nm or more. Furthermore, considering sputtering efficiency, the ITO film thickness is preferably no more than 800 nm, and considering efficiency still further, it is preferably no more than 600 nm.

From the result of this experiment, it can be seen that in a heat insulated container 10 covered with an ITO film formed by sputtering ITO in an atmosphere of an argon to oxygen weight ratio of 76 to 7, in the case where the average particle diameter of the surface particles is 50 nm or more, even after six hours, a heat retaining performance of at least 60° C. will be maintained. Moreover, it can be seen that in the case where the ITO film thickness is 150 nm or more, even after six hours has elapsed a heat retaining performance of at least 60° C. will be maintained.

EXAMPLE 2

An investigation was made into the relationship between: the average particle diameter (ITO particle diameter) of the surface particles of an ITO film; the thickness of the ITO film; and the heat retaining performance of a finished product of a heat insulated container provided with an internal container covered with that ITO film, for the case where the ITO had been sputtered onto the external surface of the internal container 12 in an atmosphere where the weight ratio of argon to oxygen was 76 to 12.

Graph A in FIG. 3 is a graph showing the relationship between heat retaining performance and ITO particle diameter, with the heat retaining performance (° C.) of a heat insulated container on the vertical axis, and the ITO particle diameter (nm) on the horizontal axis. Moreover, as with FIG. 2, on the left side of the graph, a heat retaining performance scale is shown. As this graph A shows, even under different conditions from those of example 1, it can be seen that in the case of a heat insulated container in which the external surface of the internal container is covered with an ITO film with surface particles of an average particle diameter of 50 nm or more, even after 6 hours, the temperature of the hot water can be maintained at 60° or more. Moreover, as with example 1, even if the particle diameter increases, the temperature retaining performance does not increase proportionately, and above 120 nm, the influence of particle diameter on heat retaining performance becomes smaller. In particular, over 150 nm, even if the particle diameter is increased, there is almost no change in the heat retaining performance. Therefore, under the conditions of the present example, the particle diameter is preferably 50 nm or more, and more preferably 60 nm or more. Furthermore, considering sputtering efficiency, the particle diameter is preferably no more than 150 nm, and considering efficiency still further, it is preferably no more than 120 nm.

Furthermore, graph B is a graph showing an approximation formula found from actual measured values, of the relationship between the ITO film thickness and the ITO particle diameter, with the ITO film thickness (nm) shown on the vertical axis, and the diameter of the ITO particles (nm) shown on the horizontal axis as in graph A. The right hand side of the graph shows a scale of the ITO film thickness. According to this graph, a particle diameter of 50 nm corresponds to a film thickness of 150 nm, a particle diameter of 60 nm to a film thickness of 200 nm, a particle diameter of 120 nm to a film thickness of 500 nm, and a particle diameter of 150 nm to a film thickness of 600 nm. Therefore, expressing the conditions of the above particle diameters as film thicknesses, the ITO film is preferably 150 nm or more, and more preferably 200 nm or more. Furthermore, considering sputtering efficiency, the ITO film thickness is preferably no more than 600 nm, and, considering efficiency still further, it is preferably no more than 500 nm.

From the result of this experiment, it can be seen that in a heat insulated container covered with an ITO film of ITO sputtered in an atmosphere of an argon to oxygen weight ratio of 76 to 12, in the case where the average particle diameter of the surface particles is 50 nm or more, even after six hours, a heat retaining performance of at least 60° C. will be maintained. Moreover, is can be seen that in the case where the ITO film thickness is 150 nm or more, even after six hours has elapsed a heat retaining performance of at least 60° C. will be maintained.

FIG. 4 is enlarged photographs of the surfaces of ITO films. As these photographs show, the particles of the ITO film surface are not only spherical, and particles of differing sizes are mixed together. Particularly where the particles become as large as approximately 0.2 μm for example, compared with particles of approximately 0.06 μm, the shape may become elliptical or polygonal, and the size becomes varied. In the present specification, the average particle diameter of the particles on the ITO film surface refers to the average diameter of a particle of average size, as shown in the photograph.

The preferred embodiment of the present invention has been described above, however the present invention is not limited to the above embodiment, and various modifications are possible. 

1. A heat insulated container formed by coating a radiation preventing film on at least one surface of an external surface of an internal glass container and an internal surface of an external glass container, disposing said internal container inside said external container with a gap provided therebetween, joining an opening area of said internal container with an opening area of said external container, and evacuating said gap to a vacuum and sealing it, wherein said heat insulated container is formed such that an average particle diameter of particles on the surface of said radiation preventing film is a predetermined value or more, and heat insulation performance can be evaluated from said particle diameter.
 2. A heat insulated container formed by coating a radiation preventing film on at least one surface of an external surface of an internal glass container and an internal surface of an external glass container, disposing said internal container inside said external container with a gap provided therebetween, joining an opening area of said internal container with an opening area of said external container, and evacuating said gap to a vacuum and sealing it, wherein said heat insulated container is formed such that an average particle diameter of particles on the surface of said radiation preventing film on a part present in at least a side portion of said heat insulated container is a predetermined value or more, and heat insulation performance can be evaluated from said particle diameter.
 3. A heat insulated container according to claim 1 wherein said predetermined value is 50 nm.
 4. A heat insulated container according to claim 1, wherein a film thickness of said radiation preventing film is 150 nm or more.
 5. A heat insulated container according to claim 1, wherein said radiation preventing film is an ITO film.
 6. A heat insulated container formed by coating a radiation preventing film on at least one surface of an external surface of an internal glass container and an internal surface of an external glass container, disposing said internal container inside said external container with a gap provided therebetween, joining an opening area of said internal container with an opening area of said external container, and evacuating said gap to a vacuum and sealing it, wherein an average particle diameter (x) of particles on the surface of said radiation preventing film, and a film thickness (y) thereof, have a relationship: y=4.4 x −43, where x is between 50 nm and 200 nm.
 7. A heat insulated container formed by coating a radiation preventing film on at least one surface of an external surface of an internal glass container and an internal surface of an external glass container, disposing said internal container inside said external container with a gap provided therebetween, joining an opening area of said internal container with an opening area of said external container, and evacuating said gap to a vacuum and sealing it, wherein an average particle diameter (x) of particles on the surface of said radiation preventing film on a part present in at least a side portion of said heat insulated container, and a film thickness (y) thereof, have a relationship: y=4.4 x−43, where x is between 50 nm and 200 nm. 